shackspace

When [Robert] is presented with a challenge, he doesn’t back down. His friend dreamed of reusing some old LED panels by mounting them to the ceiling of the friend’s night club. Each panel consists of a grid of five by five red, green, and blue LEDs for a total of 75 LEDs per panel. It sounded like a relatively simple task but there were a few caveats. First, the controller box that came with the panels could only handle 16 panels and the friend wanted to control 24 of them. Second, the only input device for the controller was an infrared remote. The friend wanted an easy way for DJ’s to control the color of the panels and the infrared remote was not going to cut it. Oh yea, he also gave [Robert] just three weeks to make this happen.

[Robert] started out by building a circuit that could be duplicated to control each panel. The brain of this circuit is an ATtiny2313. For communication between panels, [Robert] chose to go with the DMX protocol. This was a good choice considering DMX is commonly used to control stage lighting effects. The SN75176 IC was chosen to handle this communication. In his haste to get this PCB manufactured [Robert] failed to realize that the LED panels were designed common cathode, as opposed to his 25 shiny new PCB’s which were designed to work with a common anode design. To remedy this, he switched out all of the n-channel MOSFET with p-channel MOSFET. He also spent a couple of hours manually cutting through traces and rewiring the board. After all of this, he discovered yet another problem. The LED’s were being powered from the same 5V source as the microcontroller. This lead to power supply issues resulting in the ATtiny constantly resetting. The solution was to add some capacitors.

The members of Shackspace got their hands on an antiquated robot arm. It’s a Mitsubishi Movemaster RM-101 and was probably manufactured in the mid 1980’s. There’s almost nothing out there that tells you how to use the thing, and so they set out to figure out how to control the hardware.

This is a great example of how an EPROM dump can be really useful. After further inspection the team discovered that the arm is driven by a Z80 processor whose program is stored on an EPROM. The first thing the guys did was dump the memory since the aging storage will be useless if just a few bits become degraded. This dump will be really useful for others whose chip has already given up the ghost. The data from that dump was disassembled and painstakingly pawed through to figure out what commands were being sent to the arm. This technique worked, as the team was able to re-implement the control protocol and has already used the arm for some light painting and pen plotting (seen above). After the break you can see a control demonstration.